Peppers are rated based on Scoville Units, a method developed by Wilbur Scoville in 1912. The original method used human tasters to evaluate how many parts of sugar water it takes to neutralize the heat. Nowadays human tasters are spared and a new process called HPLC, or High Performance Liquid Chromotography measures the amount of capsaicinoids (capsaicin) in parts per million. Capsaicin is the compound that gives chiles their heat. The chart below rates chile peppers, at the bottom being mildest and the top being the hottest heat.